The Bloodstone Chalice

The Bloodstone Chalice is available only in the Dawnguard DLC and is part of the Vampire Lords questline. This quest is not available unless you accepted Harkon's gift of immortality and became a Vampire Lord.

Walkthrough

Find Garan Marethi in the castle and speak to him. Follow him until he hands you the Bloodstone Chalice, which you must fill with the waters at Redwater Spring. Redwater Spring is located in the southeastern portion of the map. You'll first be guided to Redwater Den, which is occupied by some shirtless brigands and Skooma junkies.

Head down the trapdoor into the den. The doorman imparts some words of warning before letting you in. In order to proceed any further (unless the desire is to take a quick hit of their special brew Skooma), pick the lock on the Adept-level lock to access a new area of the drug den.

People will not react to kindly to trespassing; you'll soon find yourself fighting against other Vampires and other bloodsucking minions. Make your way to the upper floor of the main cavern and activate the level to lower the bridges to cross.

Search for a chain lever that permits access to the deeper parts of the den to finally reach Redwater Spring. Once you're through the first iron door, watch out for pressure-sensitive tiles on the floor that spring spikey wall traps. Avoid these and continue through the next iron door to enter a large chamber.

You encounter many more enemies, including one named Venarus Vulpin. This named Vampire will turn invisible at low health, but remember that you can still spot his glowing hands. He drops the Redwater Spring Key that unlocks the master-level iron door lock.

Fill the chalice with the glowing red liquid. As you turn to leave, a pair of named Vampires ambush you in attempt to intercept your giving the Chalice to Harkon. Defeat Stalk and Salonia Caelia. Separate them and deal with one at a time.

After defeating the pair, scoop some of their blood into the Chalice and return to Castle Volkihar to speak with Garan. Then follow up with Harkon.